Training Module #12: Joints - Edge Joints (Click-Along)

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Database: Training Module #12 - Joints - Edge Joints_[Version#].hdb3

Project: Edge Joints - Fuse Wing

The model for this tutorial is part of a fuselage with an integrated wing. By going to the View tab of the Ribbon and selecting the "Scale Reference Model", we can see that the model size is comparable to a commercial aircraft.

We can also see that this model has also been organized into Zones and Structures. We can more easily see where we want to create Edge Joints by coloring the model by Structure. To do this:

In this color mode, we can see the fuselage is split up into a center portion and two outer portions, forward and aft, respectively. Each fuselage part has already been sequenced to generate Global Plies from the existing Sizing results. By reviewing these Plies, you can see the boundaries of these parts have discontinuous Plies. To see those:

You will notice a similar discontinuity on the other side of the center fuselage section. We will create Edge Joints at these locations to simulate splice joints between these sections.

Edge Joints are defined on the boundary between two Zones. So, to create the Joints on the center section of the fuselage, first we will switch our selection mode to "Boundaries".

To do that:

This will show all of the Zone intersections in the model. 

We will create only a handful of Joints at first to more quickly illustrate the creation process. To start, select a few on the border between the center and one of the outer fuselage sections (as shown below), right-click, and "Create Joint".

This will open the "Create Joint" form. The Viewport will also show arrows pointing from the Joints based on the current selections in that form; these represent the pull-off direction of the Joint. Additionally, the Zones on either side of the joint have been color-coded to match those on the form to show which Zone will be which member. 

The membership defined here determines how HyperX will process the loads on either side of the defined boundary. - specifically, the skin over the joint. 1 Member joints should be used when the skin is discontinuous over the joint. 2 Member joints should be used for continuous skin joints.

You can find diagrams and load equations for these in the quick help of a Joint Design Property. To view those: locate a Joint Design Property in the Library, right-click, select "Edit", and click the blue quickhelp "i" on that form. For more information, see Edge Joint Loads.

In our case, we will set up splice joints by creating back-to-back 1 Member Joints. To do this:

Once the Joints are created, you can see the model updates to show them. These Joints are now Structures which can be selected in the Viewport or the Structures Tree.

To create the outer fuselage joints, we will basically do the same thing as the last step in the opposite direction.

In summary:

At this point, we have created splice joints at these locations that are represented by two, 1 Member Edge Joints pointing in opposite directions - which represents our two sets of plies coming together at the same boundary, rather than a single set of plies flowing over top of the joint in a continuous skin. We can now assign Properties to these Joints so they can be Analyzed. 

But first, let's create Joints at the rest of the splice locations between the center and outer fuselage sections.

Repeat the previous steps on the rest of the splice locations along the fuselage.

Once all of the Joints have been created, we need to assign Properties to them so they can be Analyzed.

In the following steps, we will have to select all the Joints that we created so we can assign Properties and run Analysis/Sizing. While they can all be selected in the Viewport, it is easier to select them in the Structures Tree.

All of the Joints we've created so far have been added to their corresponding skin Structures. Their names (ordered by ID) are:

You can notice that each of these Structures contain children Structures called, "Edge Joints 1 Member". Selecting all of those (by shift-clicking them) will select all of the Joints we've created.

Tip

By searching for "edge" in the Structure Tree, it will show just these Structures and the Joints. This makes it easier to select them all quickly.

Before we can run Analysis, we need to assign 3 Properties to all of the Joints: Design, Load, and Analysis. Let's start with the Design Property.

Locate the "Single Shear - Bolted - 927" Design Property in the Property Tree. Right-click and select "Edit" to review.

On the resulting form, there are several things to notice:

To view the data stored and used by HyperX for this analysis, open the Fastener definition form for the Fastener selected (indicated in Step 4 above). On the "Fasteners" form, right-click and "Edit..." the HL11-8 Fastener. On the resulting form, you can notice that these fasteners have a 100-degree countersink and include tension and shear allowables.

Finally, notice that we have assigned a bolt material that allows for a reference temperature. In the event that a design case specifies a temperature, the tension and shear allowable will be knocked down by the \(F_{tu}\) and \(F_{su}\) knockdowns, respectively, from the Material.

After reviewing these forms, close them. With all of the Joints selected, assign this Design Property by right-clicking it in the Property Tree and selecting "Assign to Visible Selection".

The selections in the Viewport will change color temporarily to confirm the change and you can look at the Joints in the Structures Tree and see they no longer say "Unassigned".

Next, let's assign a Load Property. In the Property Tree, locate "Element Based - 1" under "Loads" > "Loads - FEA". While all Joints are selected, right-click that Property and "Assign to Visible Selections".

When we run Analysis, this Property will assess margins for every Design Load Case at every element (i.e. each joint in each direction at every location).

Finally, we must assign an Analysis Property. First, let's review the one that we will assign.

Locate "Joint Analysis Property 12" in the Property Tree under "Analyses" > "Joint". Right-click and select "Edit".

That will open the Analysis Property form which shows the Failure Modes that make up the Property. Right-click on the "Fastener 17" Failure Mode and select "Edit" to review it.

The following form will show the Criteria evaluated by this Failure Mode as well as additional inputs (Settings) that define various conditions for the Fastener. Notice this Failure Mode includes criteria for tension and shear on the fastener, as well as for bearing loads on the connected plates. Scrolling down on the form reveals two Settings at the bottom: "Derive fastener bending" and "Include prying force".

These settings tell HyperX to derive a bending force analytically, and compute a prying force based on the heel-toe interaction from the eccentricity in the shear offsets of the plates, respectively. This approach is documented in the moment supplement of Bruhn where the bending is derived from the shear offset of the composite to the plate and then an overturning bolt moment is computed and used to derive the bolt pry force from the heel-toe. For more information, see Fastened Joint Criteria.

When you're done reviewing this Failure Mode, close the form. Then right-click and "Edit" the other Failure Mode ("Fastened Sheet Strength 18").

This shows that we are including Criteria for Bearing-Bypass. This is likely to be fairly critical once we run Analysis. When you're done reviewing this Failure Mode, you can close this form and the Analysis Property form.

Ensure all the Joints are selected and assign the "Joint Analysis Property 12".

Now that we've assigned Design, Load, and Analysis Properties, we can Analyze the Joints.

To do this: Select all of the Joints, right-click on the selection in the Structures Tree or Viewport, and select "Size".

When Analysis is done, we can use the Legend to review the results.

Most of the Joints have negative margins of safety. Let's look at the controlling criteria to start figuring out why. Select the "Controlling Criterion" checkbox in the options window.

Every Joint is bearing-bypass critical. This isn't a huge surprise in this type of joint. Let's look at the composite material we've been using to see what's informing this method.

In the Library, double-click or right-click > show "Composites".

We are using "Collier Tape_" in the laminates connected to our Joints. Double-click or right-click > edit "Collier Tape_" in the "Composites" form to open the "Composite Material" form. In that form, expand the "Joints and Holes..." section and click the "Plot Bearing-Bypass Data" to view the Bearing-Bypass allowable informing this analysis.

The X-axis is the Bypass Stress; it has a negative portion for compression bypass and a positive one for tension bypass. The Y-axis is the Bearing Stress and, by hovering over the third point, you can see that the bearing stress cutoff is about 75 ksi.

Additionally, these allowables are modified by corrections which can be viewed in the Correction Factors form (see Composites > Correction Factors and Correction Data Definition). To view them, press the "Correction Factors" button on the Composite Material form.

By scrolling down to the "Bolted Joint Stress Allowables" you can see that the "Bearing" allowables are a table. Double-click or right-click and select "Correction Data Definition" on the cell to view the Correction Data Definition form.

Here you will notice a few things:

We are going to proceed with the current settings but note that you can modify these settings, add new variables, etc. to customize your corrections.

When you're done reviewing these settings, you can close these forms. Next, we will try to resolve the negative margins by updating the Joint Design Property.

To resolve a negative bearing-bypass margin, an initial instinct is to increase the thickness of the laminate.  We can do this by editing the Design Property. First, open the "Single Shear - Bolted - 927" Design Property by locating it in the Property Tree, right-clicking, and selecting "Edit".

Currently, the Sheet 1 Material and Thickness is inherited from acreage Sizing results. If we manually select a new Material, we can choose a thicker Laminate that we can test by running Analysis.

To do this:

Ensure all of the Joints are selected and re-run Analysis (right-click and select "Size"). When Analysis is complete, switch the Legend back to "Minimum MS" to view the results.

Unfortunately, quite a few negative margins remain. While we could continue trying new edge band materials/thicknesses and re-Analyzing until all of our margins of safety are positive, we can find an optimal solution more quickly with Advanced Sizing.

To set up for Advanced Sizing, we will edit the Joint Design Property again. Locate it in the Property Tree, right-click, and "Edit".

A few things to notice here:

Let's start by allowing HyperX to use any available Laminate Material when Sizing. To do this:

Next, let's notice that we already have two fastener options selected. If you right-click on those selections and choose "Select and Order Fasteners" you can see they are the HL11-8 and HL10-10. You can review these in the Fastener section of the Library.

Next, you can see that we also allow the fastener spacing and number of rows to vary. We can specify a range with a minimum and maximum value, the number of values in that range to try, and the "step size" between them. Using the "Order" column, we can also specify whether to start at the max or min and step down or up, respectively, through the range. For instance, as HyperX tries different fastener spacings based on these settings, it would start at 2 inches, then try 1.75, 1.5, 1.25, and 1 inch.

Finally, notice the order of operations defined by the "Seq..." column. HyperX will use this to guide the changes made while it attempts to resolve margins. After each change, it will re-Analyze the Joint. If the margins are still negative, it will try the next variable in the list. If margins are still negative after all operations, HyperX starts over at the next value for that variable.

Based on our current settings, HyperX will:

Now that we've finished making changes and reviewing settings, click "Apply" to save the changes and close the form.

To run Advanced Sizing, select all of the Joints, right-click, and select "Size".

Going back to the Legend, we can see that there are no more negative margins after Advanced Sizing.

Some of these margins are still low. Let's select a few of them and use the Analysis Results Watch Window to take a closer look at what is controlling these margins.

In this window, we can sort the criteria to see which are more critical than others. Unsurprisingly, we can see that we are still bearing-bypass critical on these Joints.

Because we used Advanced Sizing to achieve positive margins instead of manually changing each Joint, we don't immediately know which solution worked on each Joint. Using the options available through the Legend, we can find that out.

To see which Fasteners were used for each Joint:

You can repeat the process above for all of the variables we allowed. You can find other relevant options such as "Sheet 1 Thickness", "Fastener Rows", and "Spacing" on the "Dimensions" tab.

HyperX's Advanced Sizing allows you to quickly resolve margins by optimizing solutions with multiple variables. Then, HyperX's results visualization tools allow you to understand the solutions that were chosen and why.